My little finger could do with some work. It doesn't always sound a note clearly, and can be a challenge to stretch across the fretboard. Here are some things I'm practicing.
You'll need to use your middle and ring finger on fret 3, but it's easier to reach the 5th fret if you release it for the high note.
The book I cribbed this from says "The add9 chord changes come thick and fast in this riff, so always focus on the fret your 1st finger is moving to. The tempo also makes it essential to maintain the five-fret stretch of the left fingers at all times."
The 4th fret in bar 3 is the main focus here, but don't neglect the 6 in bar 5.
C-shape and G-shape triads are a stretch when played on the 6th and 5th string positions. Here are some progressions to exercise that. Think of each repeat section as its own separate riff, and play it repeatedly until the chord changes are smooth.
There are no open strings, so move these chords around the fretboard. Try out different rhythms too. Picking over these patterns will show you if you're not cleanly fretting certain notes.
Box 3 of the standard pentatonic pattern has a position shift when moving between the 3rd and 2nd strings. Here's a few exercises for that.
Here's the basic pattern. D is the root of the minor pentatonic (the second note in the box), hence the leading C. Roots are marked in red.
The 3-2 "trick" is a way of diagonally navigating the fretboard in a pentatonic pattern. This is a major pentatonic that uses the little finger often. There's many ways to finger it but try to use 1-2-4 consistently to practice stretching.